For chimney systems to work effectively, maintaining certain pressures may be required. In various prior art chimney systems with significant vertical and lateral runs, a draft inducer is included for low-draft situations, and an over-draft damper is included for reducing draft once the chimney has been primed and excessive draft pressures are generated. A controller uses a first feedback loop—often a proportional-integral-derivative (or “PID”) loop—to operate the draft inducer, and uses a second feedback loop—again, often a PID loop—to operate the damper. If pressure in the chimney is excessively positive, the controller increases the speed of the draft inducer to offset the excessive positive pressure. However, if the chimney system becomes excessively negative, the controller switches PID loop control to operate the damper, which baffles flue gas to reduce the excessive negative pressure.
Limitations may exist in such prior art systems. For example, the draft inducer, the damper, hardware for each PID loop, and software for each PID loop may introduce initial, operational, and maintenance costs to each system. Further, the components may collectively require a relatively large amount of space in the prior art systems. In various embodiments of the current invention, these and/or other limitations may be overcome or reduced.
Reversible draft controllers and exhaust systems incorporating reversible draft controllers are provided herein.